The present invention relates generally to blades that regulate a developer layer thickness on a development roller in a development device, methods of manufacturing the same, and dies for manufacturing the same. The present invention also relates to development devices and image-forming devices using the blade. The present invention is suitable, for example, for a blade that regulates a layer thickness of a nonmagnetic monocomponent developer on the development roller, a method of forming the layer of the nonmagnetic monocomponent developer using the blade, a development device having the blade, and an electrophotographic image-forming device having one or more of these elements. Notwithstanding, the present invention is not limited to embodiments using the nonmagnetic monocomponent developer.
Hereupon, the xe2x80x9cnonmagnetic monocomponent developerxe2x80x9d is a single component developer that is nonmagnetized and includes no carrier. The xe2x80x9celectrophotographic image-forming devicexe2x80x9d by which we mean is an image-forming device employing the Carlson process described in U.S. Pat. No. 2,297,691, as typified by a laser printer, and denotes a nonimpact printer that provides recording by depositing a developer as a recording material on a recordable medium (e.g., printing paper, and OHP film).
With the recent development of office automation, the use of electrophotographic image-forming devices such as a laser printer for computer""s output devices, facsimile units, photocopiers, etc. have spread steadily. The electrophotographic process generally uses a photoconductive insulator (e.g., photosensitive drum, and photosensitive belt), and follows the procedural steps of charging, exposure to light, development, transfer, fixing, and other post-processes.
The charging step uniformly electrifies the photosensitive drum (e.g., at xe2x88x92600V). The exposure step irradiates a laser beam or the like on the photosensitive drum, and changes the electrical potential at the irradiated area down, for example, to xe2x88x9250 V or so, forming an electrostatic latent image. The development step electrically deposits a developer onto the photosensitive drum using, for example, the reversal process, and visualizes the electrostatic latent image. The reversal process is a development method that forms an electric field by a development bias in areas where electric charge is eliminated by exposure to light, and deposits the developer having the same polarity as uniformly charged areas on the photosensitive drum by the electric field. The transfer step forms a toner image corresponding to the electrostatic latent image on a recordable medium. The fixing step fuses and fixes the toner image on the medium using heat, pressure or the like, thereby obtaining a printed matter. The post-processes may include charge neutralization and cleaning on the photosensitive drum from which toner has been transferred out, a collection and recycle and/or disposal of residual toner, etc.
The developer for use with the aforementioned development step can be broadly divided into a monocomponent developer using toner and a dual-component developer using toner and a carrier. The toner may be a particle prepared, for example, in such a manner that an additive and a colorant such as a dye and a carbon black, or the like are dispersed in a binder resin made of synthetic macromolecular compound, and then is ground into a fine powder of approximately 3 through 15 xcexcm. The additive, which is a fine particle used as a toner surface reforming agent, has been used originally for improving fluidity of toner, but sometimes for improving image quality. The additive may be selected among colloidal silica, titanium oxide, alumina, zinc stearate, and others. A usable carrier may include, for example, an iron powder or ferrite bead of approximately 100 xcexcm in diameter. The monocomponent developer advantageously results in (1) simple and miniature equipment due to omitting mechanisms for controlling a carrier deterioration and toner density, and mixing and agitation mechanisms, and (2) no carrier or other waste in used toner.
The monocomponent developer may be further classified into a magnetic monocomponent developer in which toner contains a magnetic powder, and nonmagnetic monocomponent developer in which toner does not contain the same. However, the magnetic monocomponent developer is disadvantageous in (1) the low transfer performance due to the high content of low electrical resistant magnetic powder which hinders the increase of the electric charge amount, (2) the difficulty in colorization due to its black-color magnetic powder of low transparency; (3) the low fixing performance, which thereby requires high temperature and/or high pressure, due to the magnetic powder, increasing a running cost. Accordingly, the nonmagnetic monocomponent developer without these disadvantages is expected to be in increasing demand in future.
For the nonmagnetic monocomponent developer, the toner having a relatively high volume resistivity (e.g., at 300 Gxcexa9xc2x7cm, etc.) is commonly used. In addition, the toner, as basically carries no electric charge, needs to be charged by the triboelectricity or charge injection in the development device.
The development process employing the nonmagnetic monocomponent developer is divided into contact- and noncontact-type development processes: The contact-type development process deposits a developer on the photosensitive drum by bringing the development roller carrying the developer into contact with the photosensitive drum; and the noncontact-type development process providing a certain gap (e.g., of about 350 xcexcm) between the development roller and the photosensitive drum to space them from each other, and flies the developer from the development roller and deposits the same onto the photosensitive drum.
It is significant for the development process employing the nonmagnetic monocomponent developer to ensure a sufficient image density by controlling the amount of toner fed from the development roller to the photosensitive drum. Thus, it is very important to form a specified toner layer through controlling its thickness on the development roller. As a typical method for regulating a toner layer thickness, it has conventionally been proposed to provide an elastic blade (restriction blade) in contact with the development roller to maintain the layer thickness uniform.
The contact-type development device employing the typical nonmagnetic monocomponent developer generally comprises a reset roller, a development roller, and a blade. The development roller is connected with a bias power supply from which the development bias is applied. The reset roller, which is also called supply roller or application roller, comes in contact with the development roller and serves not only to supply toner to the development roller, but also to scrape off and remove the toner unused for the development and remaining on the development roller. The development roller, which is, for example, a roller made of resin, adsorbs the charged toner onto its surface in the form of a thin layer, and conveys it to a development area in contact with the photosensitive drum.
The blade is brought into contact with the development roller and serves to regulate the toner layer to a uniform thickness. The blade may be made up of a metal member, or of an elastic member such as urethane, and regulates the toner layer by bringing an end portion or non-end portion (namely midsection) thereof into contact with the development roller. Disadvantageously, too thin toner layer would lead to reduced and varied image densities, and too thick toner layer would increase the ratio of the toner having reverse charge or low charge, and produce fogging (a phenomenon of undesirably coloring with the toner areas that have no image and thus are expected to be of white clarity). Accordingly, the blade is required to form a toner layer having an adequate thickness.
A description will be given of a regulation of the toner layer thickness by the blade, when the blade brings its end portion into contact with the development roller, with reference to FIG. 28. Hereupon, FIG. 28 is a schematic sectional view for showing a relationship between curvature of the blade and the regulated toner layer, where the blade 500 includes an end portion 510 (any one of end portions 512-516) which may have three different values of curvature. If the blade 500 includes the end portion 512 having the smallest curvature, the blade 500 is too deeply engaged in the development roller 20, and the thickness of the toner layer T (i.e., height from the surface of the development roller) becomes thin, as represented by the dash-single-dot line in the drawing. On the other hand, if the blade 500 includes the end portion 516 having the largest curvature, the blade 500 is too shallowly engaged in the development roller 20, and the thickness of the toner layer T becomes thick, as represented by the broken line in the drawing. An adequate thickness of the toner layer may be obtained where the blade 500 includes the end portion 514 having curvature indicated by the solid line. As described above, the blade 500 needs to include the end portion 510 having adequate curvature.
As a method of forming such an end portion having adequate curvature on the blade, the present inventors have disclosed, in Japanese Laid-Open Patent Application, Publication No. 9-62096 (U.S. Pat. No. 5,867,758), a technique to form the end portion 514 utilizing a shear drop that inevitably formed in a blanking process. The blanking is carried out using a blanking die that includes a die and a punch, and upon blanking, a shear drop is formed at the end portion 510, and a burr (or flash) is formed at an end portion 520 opposite to the end portion 510. The shear drop means a curved portion formed upon shearing, and the burr means an acutely angled end portion formed upon blanking. The dimensions of the shear drop has conventionally been configured to be smaller than those of the end portion 512, but the present inventors has disclosed in the above publication that the dimensions of the shear drop may be made larger by making a clearance between the die and punch wider than a conventional distance.
In operation of development, the toner is charged (e.g., negatively) using sliding friction among the reset roller, the blade, and the development roller. The negatively charged toner thereafter is fed onto a surface of the development roller by the reset roller, and deposited thereon by electrostatic adsorption. Subsequently, the toner layer on the development roller is leveled with the blade to form a thin layer having a uniform thickness of about 10 xcexcm through 40 xcexcm. The toner is conveyed from the photosensitive drum to the development roller, and adhered to an electrostatic latent image on the photosensitive drum with the electrical force of attraction by a predetermined voltage applied to a development area. Consequently, the latent image is visualized and developed. Next, the reset roller removes the residual toner on the development roller that is left in a no-image area where no latent image is formed. The development process repeats a series of these operations.
However, the idea seized upon the present inventors that the manufacturing method and the resultant blade disclosed in Japanese Laid-Open Patent Application, Publication No. 9-62096 still had several disadvantages, and thus an improvement of the manufacturing method should be necessary.
First, the manufacturing method in the publication would shorten the life of the blanking die. It is because the wide clearance is allowed in the blanking die beyond the range conventionally considered to be suitable for blanking, overloading the blanking die.
Second, the manufacturing method in the publication would have difficulties in controlling the dimensions of the shear drop, and if the dimensions of the shear drop were those depicted as the end portion 516, image quality would become deteriorated. This is because the dimensions of the shear drop depend upon not only the sharpness of the edge of the die but also the hardness of the blade material, which is difficult to be adequately adjusted.
For instance, the edge of the die, immediately after ground, would be too sharp and thus form too small shear drop, so that the wasted blanking of around five thousands sheets of the material would be required for providing a specified sharpness with the die. This would result in reduced yields and increased costs.
Similarly, varied hardness of the blade material would lead to poor reproducibility, and reduced yields and increased costs as well. To be more specific, the end portion 510 may be represented by a height X and length Y (Y1 and Y2) of a curve thereof, and the manufacturing method in the publication uses the height X as the reference when the end portion 510 is formed. Hereupon, FIG. 29 is a schematic partially enlarged section of a conventional blade 500. In order to obtain a desired height X, for instance, a relationship between the clearance and the height X is established, and the clearance is adjusted to a necessary distance. However, the present inventors later discovered that the wearing out in the end portion 510 proceeds so as to reduce the length Y instead of the height X. For instance, the length Y1 becomes the length Y2 due to the wearing out, in FIG. 29. However, the length Y of the blade obtained by the manufacturing method in the publication also cannot accurately be determined due to a wide range of variations according to the hardness of the material. As a matter of course, the manufacturing method in the publication cannot provide any information on the resultant blade such as a relationship between the height X and the length Y, and a relationship between the clearance and the length Y. Therefore, it is the information on the clearance required for attaining a certain height X, but not the information on the length Y that can be provided in the manufacturing method in the publication. Since the height is not worn out, and the end portion 510 depends upon the length Y; in other words, the manufacturing method in the publication provides low reproducibility of the blade including the desired end portion 514.
On the other hand, even such a blade as initially includes the end portion 514 having an appropriate curvature would wear out due to a continuous use to become shaped like the end portion 516, and make the toner layer thick. The present inventors, having studied the cause thereof, finally discovered that they did not then consider a relationship between hardness of a blade material and that of an inorganic substance (e.g., external additive) that is added to toner. Particularly, in recent image-forming devices that require high-speed printing operation, the development roller rotates at high speed, and thus an increased load is likely to be imposed on the blade.
Accordingly, it is an exemplified general object of the present invention to provide a novel and useful blade for use with a development device, method of manufacturing the same, die for manufacturing the same, development device and image-forming device having the same in which one or more of the above disadvantages in the prior arts are eliminated.
Another exemplified and more specific object of the present invention is to provide a blade for use with a development device, method of manufacturing the same, die for manufacturing the same, development device and image-forming device having the same that may stably form high-quality images.
In order to achieve the above objects, the inventive stamping die comprises an upper mold portion and lower mold portion that includes a punch and is movable relative to the upper mold portion, and the knockout includes in cross section a first flat portion and a triangular projection portion that projects from the first flat portion. The punch includes in cross section a second flat portion and a triangular groove portion formed on the second flat portion, and a first angle at which the triangular projection portion projects from the first flat portion is larger than a second angle at which the triangular groove portion is recessed from the second flat portion. Alternatively, or optionally, the above knockout includes in cross section a first flat portion and a triangular projection portion that projects from the first flat portion, while the above punch includes in cross section a second flat portion and a triangular groove portion formed on the second flat portion, and a first width of a joint between the triangular projection portion and the first flat portion is smaller than a second width of the triangular groove portion viewed from the second flat portion. Further, alternatively or optionally, the above knockout includes in cross section a first flat portion, the punch includes in cross section a second flat portion, any one of the knockout and the punch includes a projection portion that projects from any one of the first flat portion and the second flat portion, the other of the knockout and the punch includes a groove portion formed on the other of the first and second flat portions, and the projection portion and the groove portion have different dimensions. Furthermore, the blade as one exemplified embodiment of the present invention is manufactured using any one of these stamping die.
These stamping die experimentally includes a base portion and a specified curved end portion, and can manufacture a blade usable for regulating a layer thickness of developer. The end portion of the blade includes in cross section a height and a length, and one or more of the stamping dies, for example, can manufacture the blade in which an approximately specific relationship is established for each thickness between the height and the length in the end portion. In addition, one or more of the stamping dies can manufacture the blade in which an approximately specific relationship is established between the length in the end portion and the second angle irrespective of the hardness of the blade material. Moreover, one or more of the stamping dies can manufacture the blade in which an approximately specific relationship is established for each thickness of the base portion of the blade between the length of the end portion and the second angle.
The inventive development device including a development roller and the aforementioned blade also has the same effects as the above blade. Similarly, the inventive image-forming device including a photosensitive body, a charger that charges the photosensitive body, an exposure part that exposes the photosensitive body charged by the charger, and forms an electrostatic latent image, the above development device that develops the exposed photosensitive body and visualize the electrostatic latent image into a toner image, and a transfer part that transfers the toner image onto a recordable medium also has the same effect as the above blade.
A development device as another exemplified embodiment of the present invention comprises a development roller, and a blade that is brought into contact with the development roller, and forms a layer of developer on the development roller with a predetermined layer thickness, the developer includes toner and an inorganic fine particle, and the blade includes a portion that has higher hardness than the inorganic fine particle and comes in contact with the developer. This development device can maintain the predetermined layer thickness on the development roller, as the blade is not worn out by the inorganic fine particle. The inventive image-forming device including a photosensitive body, a charger that charges the photosensitive body, an exposure part that exposes the photosensitive body charged by the charger, and forms an electrostatic latent image, the above development device that develops the exposed photosensitive body and visualize the electrostatic latent image into a toner image, and a transfer part that transfers the toner image onto a recordable medium also has the same effect as the above development device.
A method of manufacturing a blade as one exemplified embodiment of the present invention comprises the steps of placing a sheet material in a lower mold portion of a stamping die, in which said stamping die comprises an upper mold portion including a knockout, and the above lower mold portion including a punch, and movable relative to the upper mold portion, the knockout including in cross section a first flat portion, the punch including in cross section a second flat portion, any one of the knockout and the punch including a projection portion that projects from any one of the first flat portion and the second flat portion, the other of the knockout and the punch including a groove portion formed on the other of the first and second flat portions; bringing the upper mold portion and the lower mold portion near to each other; bringing the knockout and the punch relatively near to each other; bringing the knockout and the punch relatively apart from each other; and bringing the upper mold portion and the lower mold portion apart from each other. It has been experimentally shown that this method of manufacturing a blade can manufacture a blade including a specified end portion by using the above-described stamping die.
Other objects and further features of the present invention will become readily apparent from the following description of the embodiments with reference to accompanying drawings.